Approximately 20-30% of a vehicle's fuel consumption relates to its tires. Vehicular tires have a tendency to resist rolling while in operation, due at least in part to adhesion of the tire's rubber to the road it is rolling on. Vehicles overcome the rolling resistance of tires by producing more energy, thereby burning more fuel. Low rolling resistance tires require less energy as the tire rolls, thereby increasing a vehicle's fuel efficiency. Reducing rolling resistance in tires is therefore desirable for cars configured to meet today's increasingly demanding standards for lower fuel consumption and reduced carbon dioxide emission.
Tire manufacturers have taken a number of approaches to developing and manufacturing low rolling resistance tires. For example, incorporation of functionalized elastomers into vehicular rubber tires can improve tire performance properties. The functional groups can act to modify the interaction of the elastomer with the fillers that are also present in tires, primarily silica. Functionalization of elastomers can be achieved either during or after polymerization. Functionalization during polymerization uses functional monomers, initiators, or termination agents. Functionalization during polymerization, i.e., co-polymerization and/or chain-end functionalization, has several known disadvantages. For example, copolymerization often requires complex syntheses to make the functional monomers. A further limitation is the choice of suitable functional groups for functionalization during polymerization, as the functional groups are limited to those that do not react with the polymerization initiator. Chain-end functionalization can be accomplished, but due to the relatively high molecular weight of the tire rubber, the weight ratio of end groups to main chain can be too low, so that the end groups do not significantly impact the elastomer-filler interaction.
Post-polymerization functionalization can be achieved by a variety of methods. For example, silane coupling agents can be used in conjunction with silica fillers. Use of the silanes, however, can lead to an undesirable increase in composition viscosity during tire manufacturing.
There remains a need in the art for improved rubber that can overcome the above-described technical challenges, in particular, rubber compositions that include functionalized elastomers that can improve tire performance properties.